CVE-2026-69356: Microsoft Exchange Server Spoofing Vulnerability

Overview

Severity

Critical (CVSS 9.3)

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N/E:U/RL:O/RC:C

Category

Spoofing

Exploit Status

Not Exploited

Exploitation Likelihood

Less Likely

Patch Tuesday

2026-Sep

Released

2026-09-08

EPSS Score

0.76% (percentile: 54.7%)

Description

Improper neutralization of input during web page generation ('cross-site scripting') in Microsoft Exchange Server allows an unauthorized attacker to perform spoofing over a network.

FAQ

How could an attacker exploit this vulnerability? An unauthenticated attacker could send a specially crafted calendar invitation containing a malicious meeting link. A user would need to open the meeting and select the Join link; successful exploitation could allow script to run in the user's authenticated Outlook on the web session and access or modify mailbox data.

Affected Products (4)

ESU

• Microsoft Exchange Server 2019 Cumulative Update 14
• Microsoft Exchange Server 2019 Cumulative Update 15
• Microsoft Exchange Server 2016 Cumulative Update 23

Server Software

• Microsoft Exchange Server Subscription Edition RTM

Security Updates (1)

• 5121608

Acknowledgments

odgrso with <a href="https://gmo-cybersecurity.com/">GMO CyberSecurity by Ierae Inc</a>

Revision History

• 2026-09-08: Information published.